Syrian government forces recaptured territory on Damascus's eastern outskirts from rebels on Wednesday after stepping up attacks in that area, a military media unit run by Hezbollah said.

The army took control of a number of blocks in the Jobar district, and another area in Ain Terma, more than a mile to the south, the unit said in a statement.

The advances could not be immediately verified.

Syria's army and its allies have intensified attacks against rebels in areas east of the capital in recent days.

Warplanes launched more than two dozen air strikes in Jobar and Ain Terma since Tuesday, the British-based Syrian Observatory for Human Rights war monitor reported.

Air strikes hit rebel-held districts east of Damascus on Thursday for the first time in weeks.

Rebel-held areas east of Damascus are besieged by the government and its allies, which include Hezbollah and Russia. Some rebel and militant groups have also fought among themselves in recent months, which observers say makes it easier for government forces to attack and gain ground.

A family of nine were killed in a pro-government air raid on the town of Khasham in Deir Ezzor, said the war monitor, among 13 killed in the attack. Some 72 civilians have been killed in government air strikes in the month to 20 June, according to the Observatory.

SDF closing in on Raqqa

Further north, US-backed Syrian militias closed in on Islamic State's Syrian stronghold of Raqqa, taking territory on the south bank of the Euphrates River with the aim of encircling the city, a militia spokesman told Reuters.

The Syrian Democratic Forces (SDF), which include Arab and Kurdish fighters and are supported with air strikes by a US-led coalition, began an offensive two weeks ago to seize the northern city from IS, which overran it in 2014.

Nouri Mahmoud, spokesman for the Kurdish YPG militia which is part of the SDF, told Reuters that IS had been ousted from the suburb of Kasrat al-Farj as the SDF moved in along the southern riverbank from the west.

When the campaign began, the SDF had Raqqa, which sits on the Euphrates' northern bank, surrounded from the north, west and east. Although IS controlled the south bank of the river, coalition air strikes had destroyed the bridges connecting it to the city.

The SDF is now trying to enact a siege of the city by taking the southern bank. The forces are a couple of kilometres from achieving this aim.

The Syrian Observatory for Human Rights war monitor said on Wednesday SDF forces had moved along the southern river bank to reach the eastern edge of Kasrat al-Farj, in the area between the new and old bridges into Raqqa.

IS is also facing defeat in its Iraqi stronghold of Mosul and is being forced into retreat across much of Syria, where Deir e-Zor in eastern Syria is its last major foothold.